The derailleur mechanism of a rear gearing system is a vulnerable part of a bicycle. In order to protect the derailleur mechanism from being damaged when the bicycle encounters high force impacts, for example, when the bicycle is hit or falls down, some manufacturers confine the gearing system within the hub of the rear wheel of the bicycle or within the frame of the bicycle. Others use a derailleur mount for protecting an externally built derailleur mechanism. Such a derailleur mount is used as a buffer that absorbs impacts and thus protects the derailleur and/or the frame of the bicycle from being damaged.
The derailleur mount may be an integral part of the frame in of some bicycles. Other bicycles, such as full suspension bicycles, are commonly equipped with a removable derailleur mount, which is designed to be replaced when damaged. Some derailleur mounts are manufactured to fit various bicycle models, whereas other hangers are custom designed for a specific model of bicycles.
Commonly, the derailleur mount is made of an alloy softer than the alloy used for manufacturing the frame of the bicycle. Thus, when the bicycle is hit, the derailleur mount absorbs the impact and bends, thus, taking the blow and preventing the frame of the bicycle from being damaged.
However, the absorption of the impact by the derailleur mount may not eliminate possible damage to the bicycle. Frequently when the derailleur mount encounters impacts with high force, it bends inwardly towards the spokes of the rear wheel, causing the derailleur to miss shift the gears and in some cases, gets into the spokes while the rear wheel is revolving, causing damage to the spokes, for example by breaking and/or bending them.
In the worse case scenario, the derailleur pulls the spokes (backwards) so forcefully that the frame part that the derailleur is attached to may severely deform or may even break.
When the derailleur mount bends, it changes the angle at which the chain runs over the sprocket, and thus, the chain can no longer intertwine with the sprocket. As a result, the chain falls off the sprocket and ends up on the next sprocket in line. Consequently, because of the derailleur mount being substantially bent the derailleur gearing system is badly damaged.
From that point, as the rider continues shifting the bicycle into the low gears, the angle at which the chain runs onto the sprocket keeps decreasing, and thus, causes the chain to shift from a smaller sprocket to a larger one. Eventually, the chain is snagged on the sides of the teeth of the larger sprocket and twists.
Ultimately, the derailleur is forced into the spokes of the rear wheel, and it is impossible to continue riding the bicycle as the derailleur and the rear wheel are destroyed. The rider may lose balance and be tossed off the bicycle.
Various attempts have been made in the past to design derailleurs and derailleur mounts that do not deform when the bicycle is hit or falls down on the ground. Some of these inventions are described hereinafter.
The following first three patents disclose derailleurs designed to withstand and absorb impacts. The forth patent discloses a shielding hanger designed to protect the derailleur from being damaged in case it is hit.
EP 0,061,365 (Huret) discloses an invention that overcomes the drawbacks of a conventional device employing a screw and a nut, in particular as concerns the mounting of the derailleur. This is achieved by providing on a support plate of the derailleur an elastically yieldable fastener, which is permanently fixed on the support plate and adapted to cooperate with the frame lug so as to ensure that the support plate remains in position relative to the frame lug. The support plate further comprises means for centering the support plate relative to the frame lug.
U.S. Pat. No. 4,734,084 (Nagano) describes a derailleur which includes a linkage mechanism comprising a fixing member fixed to the bicycle frame, a pair of linkage members pivoted to the fixing member, and a movable member carrying a chain guide and pivoted to the linkage members. The linkage mechanism is provided with a displacement structure which elastically biases the linkage mechanism axially of a multistage sprocket assembly when subjected to a force or pressure greater than a normal resistance against speed change, thereby preventing the fixing member and bicycle frame from being plastically deformed as a result of a sudden forceful impact, such as in a collision, hitting a foreign object of if the bicycle falls down.
WO 9,316,910 (Iwasaki) describes a rear derailleur for a bicycle that is small, light, low in production cost and free from damage when the bicycle falls on the ground. This rear derailleur comprises a base member supported on a bicycle frame in front of a multi-staged sprocket supported in turn around a hub shaft, an oscillating member connected to this base member at the proximal portion thereof in such a manner as to oscillate in a widthwise direction of a wheel and extending rearwardly, and a chain guide which rotatably supports a guide pulley and a tension pulley and is supported at the rear end portion of the oscillating member in such a manner as to rotate about a shaft substantially in parallel with the hub shaft while being elastically biased in a direction in which a tension is applied to the chain, wherein the guide pulley is oscillated in the widthwise direction of a wheel by drawing a speed-change operation cable connected to the above oscillating member, whereby the chain is switched to a desirable sprocket for engagement therewith.
EP 0,252,704 A2 (Kirk) discloses a bicycle frame made of lightweight alloy or metal such as magnesium and characterized in that a mounting for a chain guide sprocket for a rear derailleur comprises a bracket adapted to receive the guide sprocket mechanism in a threaded hole, and pivotally mounted on the frame so as to pivot rearwards as indicated in dashed lines from its normal position of use to create a clearance for the removal of a rear wheel mounted by means of a spindle in a slot. Optionally, the bracket is made of a plastics material, which is less structurally strong than the metal of the frame, so that the bracket will snap preferentially or sacrificially in the event of an impact, so that the frame itself will not be damaged, and the bracket merely needs to be replaced. The bracket may be somewhat yielding to absorb light impacts prior to fracture. The bracket may be pivoted onto the frame by means of a snap-in pin.
The derailleur mount described by Kirk in EP 0,252,704 A2 is made of plastic which is somewhat yielding to absorb light impacts. However, in cases of impacts, the derailleur mount may be hardly bent towards the frame of the bicycle and eventually may even break.
An aim of the present invention is to replace existing derailleur mounts, normally made of aluminum with derailleur mounts manufactured from a material sufficiently rigid to maintain the derailleur in its proper position under normal circumstances (i.e., when shifting gears), and at the same time flexible, so as to absorb the impact and return to its original shape and position.
Other advantages of the present invention will become apparent after reading the present specification and reviewing the accompanying figures.